Conventionally, a ball for ball game having a construction, where air is confined, includes a bladder made of rubber where air is confined; a reinforcing layer formed outside the bladder, by which sphericality and durability are applied to the ball; and a skin layer composed of a plurality of panels adhered onto the reinforcing layer.
There is known from the U.S. Pat. No. 4,856,781 such a reinforcing layer as to be composed of twelve fabric pieces, peripheral parts of which are sewn together to obtain a spherical shape. By virtue of the reinforcing layer, there is attained a ball where user can have an extremely soft feeling by sewing the twelve fabric pieces together to obtain a fabric layer in such a manner that only one side of the twelve fabric pieces is not sewn, and the only one side serves as a hole for introducing a bladder, reversing the fabric layer through the hole, positioning a marginal part of the hole to be located inside, introducing the bladder into the fabric layer, and sewing the hole while positioning the marginal part outside.
In the U.S. Pat. No. 4,239,568, there is disclosed a technique where a spherical fabric layer is formed by adhering a plurality of fabric pieces onto a spherical hollow body made of paraffin, forming an opening in one of the plurality of fabric pieces, collapsing the plurality of the spherical hollow body into pieces, removing the collapsed pieces from the opening, and inserting a bladder through the opening.
Also, there is known a ball generally called a hand stitched ball e.g. from the U.S. Pat. No. 3,119,618. This ball is obtained by sewing the panels in such a manner that adjacent marginal edges of the panels are folded inward and sewn together to form a spherical body, and inserting a bladder into the spherical body. In the sewn ball, a member called a backing member made of fabric is adhered to each of the panels. There is no reinforcing layer made of e.g. fabric covering the bladder.
In the construction disclosed in the above-mentioned the U.S. Pat. No. 4,856,781, the marginal part to be sewn for the hole for accommodating a bladder is located outside, whereby the spherical shape is prevented to be formed. That is, fine unevenness appearing on the surface through the panels due to the marginal part to be sewn. This phenomenon is generally known as the mirror-through effect, and causes the balls to be swayed.
In the fabric layer disclosed in the U.S. Pat. No. 4,239,568, the fabric pieces are adhered onto the spherical hollow body in such a manner that the marginal edges of adjacent fabric pieces are superimposed. The superimposed parts prevent the ball from forming a spherical shape, and fine unevenness appears on the surface of the panel. In the construction of the U.S. Pat. No. 4,239,568, the fabric pieces are not sewn together. There is not any knowledge in which the fabric layer is reversed.
Normally, a valve is the biggest element in essential elements of the bladder. In order to insert the bladder into the spherical fabric layer, the hole is required to have a size where the valve can be passed through the hole. That is, preferably the hole has a diameter of about 15 mm. The bladder is made of rubber, and have an elasticity. Accordingly, the elements of the bladder other than the valve can be easily passed through the hole by expanding and stretching them.
On the other hand, when the fabric layer is reversed, the hole is required to have a minimum diameter of about 20 mm even in the case of class 3 of the soccer ball which is the smallest soccer ball. The size of the hole for reversing the fabric layer is different from that for only inserting the bladder. The hole for reversing the fabric layer in the soccer ball is required to have substantially the same size as the size of the hole for reversing the fabric layer in the volley ball. The hole for reversing the fabric layer in the basket ball is required to have a size larger than the size of the hole for reversing the fabric layer in the soccer ball.
In the construction of the ball disclosed in the U.S. Pat. No. 4,239,568, the superimposed parts of the fabric pieces contribute to the mirror-through effect, and in order to reduce the mirror-through effect there is employed such a construction where the superimposed parts of the fabric pieces correspond to the boundaries of the panels. Nevertheless, it is impossible to completely remove the mirror-througheffect.
Further, as described in the U.S. Pat. No. 3,119,618, in the sewn ball having no spherical reinforcing layer the tensile strength in the part where the adjacent panels are sewn together is different from that in the center part of each of the panels, because the parts where the adjacent fabric pieces are sewn together using threads have a higher strength. For that reason, there is the problem that a ball having high sphericity cannot be obtained, because the central part of the panels are expanded. Further, the sphericity of the ball depends largely on the strength of the thread used for sewing the panels together. It is almost impossible to obtain the ball having homogeneous strength because of a workmanship, or a dispersion of the tensile strength even by the same workman.
The present invention was made in view of the circumstances as mentioned above. The object of the present invention is to provide a method for manufacturing a ball having a spherical fabric layer comprising a plurality of fabric pieces by which a sphericity is significantly improved, providing a hole for reversing the fabric layer through the hole in the case where all of the parts (for instance marginal parts of the plurality of fabric pieces) which prevent the sphericity are located inside to make the surface of the fabric layer completely spherical, the mirror-through effect is prevented from occurring, and accommodating a bladder through the hole; and a ball for ball game manufactured by the method.